I am using a Keysight InfiniiVision MSOX3054T Scope having Bandwidth of 500MHz and Sampling rate of 5Gsa/s.

I am learning to use the FFT Option in the scope.

Below is the waveform I captured of my QSPI Clock signal (48MHz)


My questions :

1. What is the threshold and the excursion levels (marked in red) mean? How to play around this value?
2. And how is the -4.97dBV calculated (again marked in red)? Can someone show the calculation for the -4.97dBV value?

 

The Threshold and Excursion settings are only relevant for Search of frequency peaks.
You need to slow the timebase and then adjust the Hz/div in FFT mode for more meaningful results.
Amplitude levels are dependent on signal source impedance and connection type.

If you have a sig gen or AWG use that to help get your head around FFT.

 

This might be useful -

Regards, Dana.

 

Can someone show the calculation for the -4.97dBV value?

dBv is the dB value of the peak signal frequency referenced to 1Vrms, or 20*log(Vsig/1).
Thus -4.97dBv is 564mVrms.